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Map showing study location of reviewed papers. Inset map of eastern USA, no data is lost under inset map

Map showing study location of reviewed papers. Inset map of eastern USA, no data is lost under inset map

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Coastal wetlands are significant components of the coastal landscape with important roles in ecosystem service provision and mitigation of climate change. They are also likely to be the system most impacted by climate change, feeling the effects of sea levels rise, temperature increases and rainfall regime changes. Climate change impacts on estuari...

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... an initial list of 678 papers, we identified 110 peer-reviewed original research papers that fit the search criteria. Of these, the majority of studies were conducted in the subtropics (78.4%), specifically in the USA (77.4%) where majority was from the east coast ( Fig. 1.), with only 7.2% from Europe, 5.4% from Asia and 4.5% each from Australia, and South America (Fig. 1), and only one study (S2 61) conducted across multiple ...
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... 678 papers, we identified 110 peer-reviewed original research papers that fit the search criteria. Of these, the majority of studies were conducted in the subtropics (78.4%), specifically in the USA (77.4%) where majority was from the east coast ( Fig. 1.), with only 7.2% from Europe, 5.4% from Asia and 4.5% each from Australia, and South America (Fig. 1), and only one study (S2 61) conducted across multiple ...
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... in atmospheric greenhouse gases (CO 2 and CH 4 ). Amongst papers only considering a single aspect of climate change, effects of SLR on CFWs have received significantly greater research attention (68 papers) compared to altered rainfall (six papers), extreme events (four papers; S2 57; 58; 79; 87), greenhouse gasses (S2 60), and temperature (Fig. 3, S2 86; 110). Twenty-eight papers considered combined threats of climate change, most commonly the interaction between SLR and altered rainfall regimes (Fig. 3). Eight papers investigated the effects of 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014 2016 2018 2020 Year of ...
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... the USA and globally vary based on local SLR rates and climate (Fig. 4.). Accretion rates are generally higher in brackish wetlands or salt marshes compared to TFFWs or TFMs (Fig. 4), and are up to 70% higher in the tidal marshes of Elbe Estuary, Germany, where tidal marshes, but not freshwater wetlands, appear to be keeping pace with local SLR (Fig. 4, S2 16). Historic rates of sedimentation in Estonian coastal wetlands show varied responses to atmospheric pressure and storm surges with increasing sedimentation rates since the 1960s, most likely in response to SLR, recent climate change and loss of sea ice but are also considered to be keeping up with local SLR (S2 95). Freshwater ...
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... change can affect CFWs via multiple pathways due to their low-lying topography and position within the coastal plain, but surprisingly little is known of what the effects and outcomes will be ( Conner et al. 2007;Saintilan et al. 2018). Most research to date examines effects of SLR, with the bulk of the knowledge generated over the last 9 years (Fig. 1) and mainly in the USA (Fig. 2). More broadly, however, we identified three broad aspects of CFWs that global research has focused on (I) sediment accretion and changes in elevation; (II) carbon accumulation, nutrient cycling and, sediment processes; and (III) vegetation structure, function, and distribution. Despite a diversity of ...

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... Their ability to remove nitrate (NO 3 -) from surface waters is particularly important as it helps ameliorate coastal eutrophication (Hansen et al., 2018, Jordan et al., 2011. Research considering how coastal wetlands respond to climate change stressors has predominately focused on brackish and marine systems, with less attention focused on the response of coastal freshwater wetlands (Grieger et al., 2020). However, these ecosystems are vulnerable to salinization due to sea-level rise, which can have such a significant impact on soil physicochemistry and wetland biota that ecosystem stability and functioning are threatened (Herbert et al., 2015), and ecosystem services such as NO 3 removal may be impaired (Ardón et al., 2013, Larsen et al., 2010. ...
Article
The salinization of coastal freshwater wetlands may impact the biogeochemical cycling of critical nutrients by altering soil microbial community structure and function. Nitrate (NO3–) reduction pathways appear particularly sensitive, though the interactive effects of salinization intensity and duration of exposure remain unclear. To address this knowledge gap, we performed a transplant experiment that exposed soil from a freshwater (≤0.1 ppt) wetland to oligohaline (1 ppt) and mesohaline (14 ppt) conditions for two years. In transplanted soils, we found physicochemical changes characteristic of salinization events, including elevated porewater concentrations of ammonium and sulfate and decreased soil organic matter and redox potential. Amplicon sequencing (16S rRNA) revealed that mesohaline levels of salinization caused rapid community restructuring; distinct transition communities were evident by the first sampling event (5 months) and persisted for ∼2 years (19–22 months). In contrast, freshwater communities transplanted to oligohaline conditions were highly resistant to restructuring, and it took nearly 2 years of salinization for differences to manifest. For both transplants, community shifts included changes in the distribution and abundance of taxa capable of NO3– reduction, including several groups also known for sulfur redox metabolism. Nitrate (¹⁵NO3⁻) reduction assays were performed to determine how rates were affected. Dissimilatory nitrate reduction to ammonium (DNRA) increased for all sampling events, but only under mesohaline conditions, whereas denitrification responses depended more on the duration of exposure than salinity level. These findings may be useful for determining when and how the ability of wetlands to remove nitrogen will be impacted by sea-level rise. Further, these results suggest that efforts to synthesize and generalize prior research regarding salinization effects on wetland microbial community structure and function must explicitly consider both salinity intensity and exposure length.
... It is causing large-scale degradation and loss of wetlands through direct and indirect effects of changes in temperature, precipitation and humidity, and subsequently in patterns of evapotranspiration, alterations in hydrological regimes, and increases in the frequency of extreme climate events such as floods and droughts (Erwin, 2009;Davidson, 2014). Sea level rise and the increasing frequency of tidal surges, with associated salinization of soil and freshwater resources, pose additional, more proximate but less predictable threats to coastal wetlands (Herbert et al., 2015;Grieger et al., 2020). ...
... Nevertheless, there are several impacts of climate change affecting the short-and medium-term suitability of wetland environments that our models are not able to detect. Sea level rise and the altered frequency of tidal surges could increase the risk of permanent saltwater intrusions into coastal freshwater wetlands, shifting the vegetation towards salt-tolerant associations and altering the structure and processes of coastal wetland ecosystems (Barlow and Reichard, 2010;Herbert et al., 2015;Grieger et al., 2020), with significant negative implications for our model species. Beyond climate change, these species could be impacted by the destruction and modification of natural habitats resulting from habitat loss and land-use change, but we have not evaluated these factors. ...
Article
Wetlands, one of the most biodiverse ecosystems in the world, are increasingly subjected to area loss and degradation due to land-use and climate changes. These factors impact their unique biodiversity, including numerous invertebrates that depend on them. Here we investigated the current and future habitat suitability of the aquatic spiders Argyroneta aquatica and Dolomedes plantarius. We evaluated future trends in their geographic range, aiming at assessing their extinction risk according to the International Union for Conservation of Nature (IUCN) Red List criteria, at both global and regional levels. We investigated present and future distribution ranges using species distribution models for two integrated emission scenarios (SSP1-2.6 and SSP5-8.5) and combining three general circulation models. These were combined with knowledge on species' dispersal limitation to account for the possibility that these species will not be able to move beyond the current range in the next decades. We found a significant future northern shift in the geographic range and a global reduction in habitat suitability for both species, corresponding to a loss of 28.9% for A. aquatica and 38.1% for D. plantarius in the next 10 years. The application of the IUCN criteria qualifies A. aquatica as Near Threatened and D. plantarius as Vulnerable. Regional assessments provided similar patterns of range reductions and population vulnerability across all European regions, particularly for Central-Eastern and Western Europe. Conversely, Northern Europe is expected to become a climatic refugium for both species. This work goes beyond the available studies on the conservation of these species by taking account their dispersal abilities in quantifying future trends in their habitat suitability using the most up to date knowledge. Conservation strategies should be directed towards limiting the impact of climatic and non-climatic stressors on wetlands, and towards implementing management plans and restoration programmes to increase habitat suitability and connectivity among wetland patches.
... Although SLR imposes obvious threats to all coastal wetlands, most previous wetland vulnerability assessments focused on tidal saline wetlands (e.g., salt marshes and mangroves) [11][12][13]. There are significant knowledge gaps on how freshwater and brackish wetlands respond to projected SLR [7,13]. ...
... Although SLR imposes obvious threats to all coastal wetlands, most previous wetland vulnerability assessments focused on tidal saline wetlands (e.g., salt marshes and mangroves) [11][12][13]. There are significant knowledge gaps on how freshwater and brackish wetlands respond to projected SLR [7,13]. Many regional and global monitoring and assessment frameworks, such as the high-precision rod surface-elevation table-marker horizon (RSET-MH) [14][15][16][17], mainly target mangroves and saltmarshes. ...
... Many regional and global monitoring and assessment frameworks, such as the high-precision rod surface-elevation table-marker horizon (RSET-MH) [14][15][16][17], mainly target mangroves and saltmarshes. Other wetlands, such as coastal floodplain forests, swamps, and lagoons, have received much less attention [2,13]. Globally, there is currently a lack of information on the distribution of these wetlands as well as basic information on the physiological ecology of major coastal freshwater wetland species under natural settings; the structure and dynamics of pure and mixed species communities, soil-plant interactions, biogeochemistry, hydrology, soils, wildlife habitat, primary biotic and abiotic functions; and the response of these systems to natural and human-caused disruptions. ...
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Many coastal wetlands are under pressure due to climate change and the associated sea level rise (SLR). Many previous studies suggest that upslope lateral migration is the key adaptive mechanism for saline wetlands, such as mangroves and saltmarshes. However, few studies have explored the long-term fate of other wetland types, such as brackish swamps and freshwater forests. Using the current wetland map of a micro-tidal estuary, the Manning River in New South Wales, Australia, this study built a machine learning model based on the hydro-geomorphological settings of four broad wetland types. The model was then used to predict the future wetland distribution under three sea level rise scenarios. The predictions were compared to compute the persistence, net, swap, and total changes in the wetlands to investigate the loss and gain potential of different wetland classes. Our results for the study area show extensive gains by mangroves under low (0.5 m), moderate (1.0 m), and high (1.5 m) sea level rise scenarios, whereas the other wetland classes could suffer substantial losses. Our findings suggest that the accommodation spaces might only be beneficial to mangroves, and their availability to saltmarshes might be limited by coastal squeeze at saline–freshwater ecotones. Furthermore, the accommodation spaces for freshwater wetlands were also restrained by coastal squeeze at the wetland-upland ecotones. As sea level rises, coastal wetlands other than mangroves could be lost due to barriers at the transitional ecotones. In our study, these are largely manifested by slope impacts on hydrology at a higher sea level. Our approach provides a framework to systematically assess the vulnerability of all coastal wetland types.
... The structure and distribution of coastal wetland vegetation is largely explained by biophysical regimes which include salinity, elevation, inundation and vegetative relationships, and form the environmental gradient structure of coastal wetlands (Rogers et al., 2014;Saintilan and Wilton, 2001;Woodroffe et al., 2016). Sea-level rise (SLR) has been identified as a factor driving forest retreat in some coastal wetland environments (Grieger et al., 2020;Kirwan and Gedan, 2019). With anticipated environmental change (IPCC, 2014;Justic et al., 2016;Wong et al., 2014), particularly in the coastal zone, it is imperative that the dynamics and characteristic structure of coastal wetland vegetation are understood. ...
... Wetlands in the supratidal zone (i.e. above Highest Astronomical Tide) are relatively understudied in Australia (Grieger et al., 2020;Saintilan et al., 2019). Currently, there is a lack in understanding of the structure, function, and distribution of supratidal Coastal Swamp Oak Forest (CSOF) in southeast Australia. ...
... Consequently, this community is vulnerable to changes in wetland hydrology (including SLR) (Saintilan et al., 2019). Historically, large areas of CSOF wetland have been lost in this region due to land-use change in the coastal zone, while observations of localised plant stress and/or dieback in some extant populations is of significant concern (Grieger et al., 2020;Kelleway et al., 2021). Data on the aboveground biomass structure of CSOF ecosystems is limited, though recent assessment shows aboveground biomass densities Fig. 1. A. Minnamurra River estuary and the focal study site. ...
Article
Coastal Swamp Oak Forest (CSOF), a supratidal wetland community dominated by Casuarina glauca, is a widely distributed coastal ecosystem along Australia's east coast. These wetland communities are highly valuable for providing ecosystem services, including carbon sequestration. Positioned within the supratidal zone of estuaries – and often abutting upper intertidal saltmarsh and/or mangrove – CSOF may be vulnerable to salinity intrusion and increased tidal inundation due to sea-level rise. To understand spatial patterns of vegetation composition and structure in CSOF, field-based (in-situ) and remote-sensing approaches were employed on the Minnamurra floodplain, New South Wales, Australia. In-situ vegetation surveys within 23 field plots located along seaward to landward transects revealed large variations in mean tree height (2.5–13.1 m) and tree densities (100–8700 trees/ha). Unmanned Aerial Vehicles with Structure from Motion (UAV-SfM), and airborne Light Detection and Ranging (LiDAR) approaches returned mean plot canopy height estimates ranging between 0.1 and 12.8 m. Comparison of vegetation metrics between remote sensors (UAV-SfM and LiDAR) demonstrated similar capacities (R² values > 0.85) to capture CSOF vegetation height. Comparison of field and spatial metrics elucidated a moderate correlation between the datasets for maximum canopy height (R² > 0.6) which can be partially explained by the different spatial scales of measurement among these approaches. Canopy height, Normalised Difference Vegetation Index (NDVI), and point density (i.e., vegetation density) estimates were each positively correlated with elevation above mean sea-level. This coincides with indications of plant stress and/or mortality at the seaward edge of CSOF, and in topographic depressions. These findings suggest physico-chemical gradients exert a strong control on CSOF vegetation structure and health, with implications for the current acceleration of sea-level rise. When combined, remote sensing and field-based datasets are useful to characterise and quantify CSOF structure and distribution and can therefore be employed in future assessments of this understudied ecosystem.
... Changes in salinity and hydroperiod in wetlands, in addition to the hydrodynamic effects on channels, result in ecological changes which may have geomorphic impacts. Coastal freshwater wetlands are among the environments most likely to be impacted by climate change, but there has been scant research on those impacts (Grieger et al., 2020). Tidal freshwater forests are 'sentinels for climate change' according to Stahl et al. (2018), with sea-level rise likely to lead to forest death due to saltwater intrusion and submergence. ...
Article
The fluvial‐estuarine transition zone (FETZ) of the Neuse River, North Carolina features a river corridor that conveys flow in a complex of active, backflooded, and high‐flow channels, floodplain depressions, and wetlands. Hydrological connectivity among these occurs at median discharges and stages, with some connectivity at even lower stages. Water exchange can occur in any direction, and at high stages the complex effectively stores water within the valley bottom and eventually conveys it to the estuary along both slow and more rapid paths. The geomorphology of the FETZ is unique compared to the estuary, or to the fluvial reaches upstream. It has been shaped by Holocene and contemporary sea‐level rise, as shown by signatures of the leading edge of encroaching backwater effects. The FETZ can accommodate extreme flows from upstream, and extraordinary storm surges from downstream (as illustrated by Hurricane Florence). In the lower Neuse—and in fluvial‐to‐estuary transitions of other coastal plain rivers—options for geomorphological adaptation are limited. Landscape slopes and relief are low, channels are close to base level, sediment inputs are low, and banks have high resistance relative to hydraulic forces. Limited potential exists for changes in channel depth,width, or lateral migration. Adaptations are dominated by formation of multiple channels, water storage in wetlands and floodplain depressions, increased frequency of overbank flow (compared to upstream), and adjustments of roughness via vegetation, woody debris, multiple channels, and flow through wetlands.
... Because considerable glacier loss is already underway due to historic emissions, its contribution to sea level rise is not likely to differ significantly between 1.5°C and 2°C global warming (Marzeion et al., 2018). However, even modest sea level rise can substantially alter the character of low lying coastal freshwater ecosystems, rapidly shifting them into more brackish or saline systems unable to support their characteristic freshwater biodiversity (Grieger et al., 2020). As Siegert and Pearson (2021) note, under high emissions scenarios, we cannot rule out 2 m of sea level rise by 2100, and up to 5 m by 2150. ...
... In many places, warming and increased CO 2 levels, as well as altered water and disturbance regimes, are resulting in woody encroachment and thickening of non-wooded wetland ecosystems (Saintilan and Rogers 2015). In coastal regions, however, saline intrusion has already resulted in widespread tree mortality in coastal swamps, generating 'ghost forests' (Grieger et al., 2020). ...
Article
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Freshwater ecosystems are highly vulnerable to global warming because 1) their chief drivers, water quality and flow regimes, are highly sensitive to atmospheric warming, and 2) they are already extremely threatened by a wide range of interacting anthropogenic pressures. Even relatively modest global warming of 1.5°C poses a considerable threat to freshwater ecosystems and the many critical services these provide to people. Shifts in the composition and function of freshwater ecosystems are widely anticipated with adverse consequences for ecosystem services, including those underpinning water and food security. While the extent and severity of effects is likely to be significantly reduced if global warming is limited to 1.5°C, concerted efforts to implement widely recognised priorities for policy and management are required to mitigate unavoidable impacts and reduce the likelihood of perverse outcomes of climate mitigation and adaptation efforts in other sectors—all of which rely on fresh water supply. Freshwater ecosystems and their services, including provision of fresh water, must therefore be considered first and foremost when developing and implementing any climate action.
... Four protected marshland sites in Hong Kong received the maximum HVI score for the threat of seawater intrusion. In the face of continuing global warming and rising sea levels, encroachment by halophytes such as mangroves will become more prevalent and substantial coastal freshwater marshlands will be lost globally (Langston, Kaplan & Putz, 2017;Schuerch et al., 2018;Grieger et al., 2020). In fact, the vulnerability assessment found that between 1996 and 2016 four coastal sites had been invaded by halophytes, such as the mangrove fern (Acrostichum aureum) and the mangrove Kandelia obovata. ...
Article
• Active and abandoned paddy fields are valuable habitats for aquatic fauna in monsoonal Asia. Changes in land use and farming practices have caused substantial losses of paddy-derived marshes in recent decades. Few of those remaining have been designated as protected areas for biodiversity or are managed for conservation. • Between 2014 and 2017, 35 paddy-derived marshes (13 protected and 22 unprotected) in Hong Kong were visited with the aim of sampling aquatic macroinvertebrates and assessing the vulnerability of sites to different threats. Twenty of them had been sampled in 1996, allowing the investigation of biodiversity change over time in relation to protection status. The representativeness of protected marshes was evaluated based on their α-, β- and γ-diversity. • In total, 272 macroinvertebrate taxa were recorded (mean, 57 morphospecies per site). Out of the 20 resurveyed sites, five (three protected) were terrestrialized and four (all unprotected) had been filled in between 1996 and 2014–2017. The relative changes in α- and β-diversity of the remaining 11 resurveyed marshes were unaffected by their protection status. • The 10 remaining protected marshes had similar α- and β-diversity to those of unprotected sites and, in total, hosted fewer species than the mean value obtained in 9,999 random selections of the same number of sites, indicating that macroinvertebrate diversity was not very well represented within the protected marshes. • Protection alone was not successful as a conservation measure because it failed to prevent the degradation and loss of paddy-derived marshlands in Hong Kong. Furthermore, a failure to consider biodiversity when the sites were designated as protected reduced the representativeness and effectiveness of the protected area network for achieving the conservation objectives. • Conservation planners need to take account of freshwater biodiversity (especially aquatic insects) during the selection of marshland sites for protection and ensure that protected sites are appropriately managed.
... coastal floodplain wetlands, freshwater swamps) largely overlooked (Williams et al. 2019). Climate change is expected to lead to sea level rise (SLR), salinisation of groundwaters, shoreline retreat, altered rainfall, warming and increased severity of extreme weather events (floods, fires, cyclones), all of which may significantly alter the composition, structure, and function of coastal freshwater wetlands (CFWs; IPCC 2014; Grieger et al. 2020), exacerbating other pressures. There is an urgent need to understand the value and environmental determinants of these poorly described ecosystems, as well as the likely effects of climate change, to guide potential adaptation strategies. ...
... Responses of saline coastal wetlands to climate-related impacts have been observed globally over recent decades, often involving altered ecosystem functioning including sediment accretion, nutrient dynamics and productivity (Tobias and Neubauer 2019;Grieger et al. 2020). Also apparent is a landward migration of communities, especially that of mangroves into saltmarsh and saltmarsh into upland or freshwater wetlands (Morris et al. 2002;Enwright et al. 2016;Schuerch et al. 2018). ...
... Non-saline coastal wetlands, hereafter referred to as CFWs, are similarly expected to be able to migrate landward in response to overland and groundwater salinisation (Boon 2012), but this has not been observed. In many situations, there is often limited space for CFWs to migrate landward due to hydrological constraints coupled with high levels of urban and agricultural development (Grieger et al. 2020). ...
Article
Coastal freshwater wetlands (CFWs) are among the most understudied wetlands globally and are highly vulnerable to projected climate changes. To address CFW knowledge gaps in south-east Queensland, Australia, we surveyed the floristic composition and structure of wooded CFWs and explored variation in vegetation patterns in relation to selected environmental drivers. Understorey and shrub assemblages were surveyed using a cover-class scale and stem counts for tree species abundance. Vegetation structure attributes (stem density, basal area) were calculated from survey data. Redundancy analysis was used to investigate drivers of vegetation structure and the species composition of each stratum. Vegetation structure patterns were associated with gradients of rainfall, soil moisture, salinity and pH. Understorey species composition was associated with wallum wetland species, native perennial grass and herb species, and vegetation patterns of the canopy. Common CFW species, namely Melaleuca quinquenervia and Eucalyptus tereticornis, dominated tree assemblage variation. Overall, CFW vegetation exhibited strong associations with gradients of salinity, rainfall, groundwater dependence and disturbance. Alterations to key drivers of vegetation pattern with future climate changes are likely to markedly influence the composition, structure and function of CFW vegetation communities. Action is therefore required to maintain CFW vegetation communities and ecological function in these diverse and unique wetland systems.
Article
Supratidal wetlands are threatened by agricultural production and are highly vulnerable to climate change, particularly through sea level rise (SLR). While vegetation structure and composition of supratidal wetlands will likely change under projected SLR with run‐on effects for ecosystem service provision, these changes can provide opportunities for restoration of adjacent agricultural land. Here, we investigated the natural regenerative potential of supratidal wetlands on abandoned agricultural land in Southeast Queensland, Australia, specifically, responses of wetland vegetation communities to simulated SLR, through tidal reinstatement. In 15 years since crop abandonment, distinct communities of typical supratidal wetland vegetation have naturally re‐established, in predominately freshwater conditions, with minimal management intervention. Reinstating tidal floodwater increased the flooded extent and permanence of brackish water. Four repeat surveys of vegetation composition, structure, and condition were conducted in permanent plots established in Casuarina swamp, Melaleuca swamp, herbaceous marsh, and riparian zone vegetation communities, to observe change over time. Species richness decreased in all regenerating communities (Herbaceous marsh, Casuarina, and Melaleuca) post flood gate removal. Understorey vegetation cover also decreased in Melaleuca and Casuarina plots, but increased in herbaceous marsh plots, with increased cover of salt tolerant species throughout. Changes in woody vegetation community and structure were not observed during this short study (2.5 years), although the regenerative capacity of woody and herbaceous species was reduced. Supratidal wetland vegetation communities can naturally re‐establish in areas of abandoned agricultural land, however, increased saltwater flooding (likely with SLR) will put these communities at risk of transition to salt‐tolerant vegetation. This article is protected by copyright. All rights reserved.